1275-1325;Middle Englishdismale unlucky time, dismol day one of two days in each month considered unlucky (hence later taken as adj.) < Anglo-Frenchdis mal < Medieval Latindiēs malī literally, evil days

Through the Middle Ages, calendars marked two days of each month as unlucky, supposedly based on the ancient calculations of Egyptian astrologers (Jan. 1, 25; Feb. 4, 26; March 1, 28; April 10, 20; May 3, 25; June 10, 16; July 13, 22; Aug. 1, 30; Sept. 3, 21; Oct. 3, 22; Nov. 5, 28; Dec. 7, 22). Modern sense of "gloomy, dreary" first recorded in English 1590s, in reference to sounds. Related: Dismally.